Heretofore, there has been known an exhaust device for vehicles which includes a catalyzer for purifying an exhaust gas that is disposed midway in an exhaust passage extending from an exhaust pipe connected to the exhaust port of an engine to a muffler on a rear portion of a vehicle body. In order to combine such an exhaust device with an oxygen sensor (O2 sensor) for detecting the oxygen concentration of the exhaust gas and feeding it back to engine control, it is necessary to consider an optimum position for the oxygen sensor as well as its relationship to the catalyzer.
Patent Document 1 discloses an exhaust device for saddle-type vehicles in which exhaust pipes connected to a plurality of exhaust port of a multi-cylinder engine are collected together below the engine and coupled to a single intermediate pipe, a muffler being connected to the intermediate pipe, a catalyzer is housed in a larger-diameter portion disposed midway in the intermediate pipe, and an oxygen sensor is installed on a portion of the intermediate pipe upstream of the catalyzer.